1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a method and apparatus for driving a liquid crystal display panel in a dot inversion system.
2. Description of the Related Art
In general, a liquid crystal display (LCD) controls light transmissivity of liquid crystal cells on a liquid crystal display panel, thereby displaying image data (a picture) that correspond to video signals.
FIG. 1 is a schematic block diagram showing a configuration of a conventional liquid crystal display panel driving apparatus employing a dot inversion system. In FIG. 1, a conventional LCD includes a liquid crystal display panel 3, a data driving integrated circuit (IC) 1 for applying a data signal to the liquid crystal display panel 3, and a gate driving IC 2 for applying a scanning signal to the liquid crystal display panel 3.
The liquid crystal display panel 3 is provided with a plurality of liquid crystal cells and thin film transistors (TFT's) for switching data signals to be applied to the liquid crystal cells. The plurality of liquid crystal cells and TFT's are arranged at intersections between a matrix array of data lines DL1 to DLp and gate lines GL1 to GLm.
The gate driving IC 2 includes multiple-stage shift registers for driving the gate lines GL1 to GLm, and responds to a gate start pulse GSP to sequentially drive the gate lines GL1 to GLm. FIG. 2 is a waveform diagram of a gate pulse applied to each of the data lines shown in FIG. 1. The gate driving IC 2 sequentially applies a gate driving pulse to the m-number of gate lines GL1 to GLm on the liquid crystal display panel 3 when the gate start pulse GSP is applied to the gate driving IC 2, thereby sequentially driving the gate lines GL1 to GLm. Accordingly, the TFT's of the liquid crystal display panel 3 are sequentially driven for each individual gate line to sequentially apply the data signals.
The data driving IC 1 includes shift registers and latches. The data driving IC 1 shifts data bits in response to a data shift clock DSC, and applies data to the data lines DL1 to DLp simultaneously in response to a data output enable signal DOE. If the data output enable signal DOE is applied to the data driving IC 1, then the data driving IC 1 applies p-number of data signals to the p-number of data lines DL1 to DLp whenever a gate driving pulse is generated. The n-number of data signals generated from the data driving IC 1 have alternating polarities in accordance with an arranged sequence of adjacent data lines. In addition, the p-number of data signals generated from the data driving IC 1 have alternating polarities converted with a lapse of frame.
FIGS. 3A and 3B depict polarities of liquid crystal cells employing a dot inversion system according to the conventional art. An LCD employs any one of line inversion, column inversion, and dot inversion systems to drive liquid crystal cells of the liquid crystal display panel. In a liquid crystal display panel driving method employing the dot inversion system, as shown in FIGS. 3A and 3B, adjacent liquid crystal cells on the gate lines and the adjacent liquid crystal cells on the data lines are supplied with data signals having opposing relative polarities, and the polarities of the data signals applied to all the liquid crystal cells of the liquid crystal display panel are inverted every frame. In other words, in the dot inversion system, when video signals at odd-numbered frames are displayed, data signals are applied to the liquid crystal cells of the liquid crystal display panel such that the positive (+) polarity and the negative (−) polarity alternate as the data signals are applied from the left upper liquid crystal cell to the right upper liquid crystal cells and to the lower liquid crystal cells, as shown in FIG. 3A. On the other hand, when video signals at even-numbered frames are displayed, the polarities of data signals applied to respective liquid crystal cells are inverted in a manner contrary to the odd-numbered frames, as shown in FIG. 3B.
FIG. 4 is a waveform diagram of a data signal and a gate pulse applied to a liquid crystal cell according to the conventional art. In FIG. 4, data signals having opposing polarities are applied to the liquid crystal cells at two continuous frames, as shown in FIG. 4. In FIG. 4, the third frame and the fourth frame during one horizontal synchronizing signal interval 1H at which a gate start pulse GSP is applied to the gate line GL receive data signals having opposing polarities.
As described above, the dot inversion system allows data signals having opposing relative polarities to be applied to adjacent liquid crystal cells in the vertical and horizontal directions, thereby providing an improved picture quality. Accordingly, the dot inversion system is conventional for driving a liquid crystal display panel.
FIG. 5 is a waveform diagram of a voltage applied to a liquid crystal cell according to the conventional art. In FIG. 5, a liquid crystal display panel that adopts the dot inversion system allows a first liquid crystal cell at two successive frames to be supplied with a gate start pulse GSP, and allows a data signal to be charged in the liquid crystal cell. Accordingly, a polarity-inverted data signal is charged in the liquid crystal cells at the two successive frames. For example, a positive (+) data signal is charged in the first liquid crystal cell at a third frame, whereas a negative (−) data signal is charged in the first liquid crystal cell at a fourth frame. In order to apply a data signal to the liquid crystal cell during a time ‘c’ at which a gate start pulse GSP is applied, a data signal is applied to charge the applied data signal into a liquid crystal cell. Accordingly, a switching time required for applying the data signal is ‘a’ and a charging time for charging the data signal into the liquid crystal cell is ‘b’.
To enhance high resolution, it is necessary to provide a high-speed driving operation, thereby reducing a width of an applied gate pulse. Thus, a horizontal synchronizing signal interval is not only shortened, but also a time at which a data signal is applied to the liquid crystal cell is reduced. In other words, since a number of data signals required to be applied at a same time becomes larger as resolution increases, a time ‘c’ at which a gate pulse is applied is reduced. Furthermore, as a number of data signals to be applied to the liquid crystal cell increases, a switching time ‘a’ required for applying the data signals is increased. Thus, a charging time ‘b’ required for charging the data signals into the liquid crystal cell is shortened.
However, in the dot inversion system, if positive (+) data signals are applied to the liquid crystal cells at odd-numbered frames, negative (−) data signals are applied to the liquid crystal cells at even-numbered frames. Accordingly, a level for switching the data signal is increased since the data signals applied to the liquid crystal cells at two consecutive frames should be converted from the positive (+) polarity to the negative (−) polarity, thereby increasing the switching time ‘a’ of the data signal. As a result, since a time ‘c’ at which a gate pulse GP is applied is fixed for each resolution, and a switching time ‘a’ of the data signal is increased, a time ‘b’ at which the data signal is applied to the liquid crystal cell should be decreased. Accordingly, the data signal is not completely charged in the liquid crystal cell, thereby distorting color or brightness of the image.